Preservation and fireproofing of wood



P atented Aug. 1,1945

UNITED STATES 2,881,049 mauve-non AND rmsrnoormc or woon menu-s Newton Hammond, unmew, Wash, as-

, Minn" a corporation signor to General Timber Service,

Inc., St. Paul, of Delaware No Drawing. Application March 18, 1939,

Serial No. scam 8 Claims.

This invention relates to the preservation and ilreprooflng of wood and particularly to an im-- proved method of introducing toxic orilreproofing materials into wood to increase its resistance to the attack of fungi and other wood-destroying organism or to make the wood resistant to fire. Either or both of these objects may be accomplished by the procedure hereinafter more fully described. 7

Wood consists of groups of cells, the walls of which are principally of cellulose. when wet, cellulose acts as a semi-permeable membrane allowing the passage. of substances in true water soiution, and preventing the passage of colloids. A cellulose membrane separating water from a watersolution will allow free passage of solvent and solute molecules through the cellulose lattice until the concentration of the solute is the same on' both sides of the membrane. If, however,

there is substantially no water on one side of the membrane, the movement of solvent and solute practically ceases. Hence'it is impracticable to-- impregnate wood with water solutions satisfac torily when the wood is dry or substantially dry, unless auxiliary. means are employed. ,Materiais which are not-water solutions do not penetrate the cell walls and can be introduced into the wood only throughthe pits cracks and checks which exist therein, and can be introduced through the side grain only by the application of pressure.- Consequently, the methods of impregnoting wood heretofore have depended primarily upon procedures involving the application of pressure to" the impregnating material, either with or without initial treatment to evacuate, so far as possible, the contents of the cells so that the 1m. "pregnating material can be forced mechanically into the wood- At best only alimited impregna- {lion' ofrnany woods can be secured by the methods eretofore used. j x

i is the object of the present invention to aflcrd a more satisfactory and practi .Q 9f mpr gnating wood with varioussolutions. adapted, because of their-toxic nature, to retard the development :of wood-destroying organisms,

or. to make the wood'ilre-resistant, or forboth tions andsubstances whi'chcan be'utilized in ac- I cordance with the method to'accomplish the purposes mentioned.

cable meth- (oi. iii-s9) The heartwood of the various woods used for construction purposes, and therefore'those which are treated to prevent destruction by fungi and other wood-destroying organisms contains only slightly more than enough moisture to saturate the wood fibres; Solutions containing toxic materials or materials adapted to make" the wood fire-resistant, will not penetrate the cell walls'of the wood to any appreciable extent by diffusion. 10 I have discovered, however, that if the :wood is first treated to increase the moisture content of the cells, the rate of diffusion of solutions containing toxic and other materials increases rapidly, and consequently it is possible without the aid is of mechanical pressure, to thoroughly impreg-'v nate the wood with the desired solutions in a relatively brief time.

Accordingly, I subject the wood, prior to its treatment with the desired solution,-to an initial treatment by soaking it in hot water fora sufli= cient length of time to eil'ect the desired increase conducted may vary over a wide range. Since temperatures below 120 F. cannot be considered effective in killing fungus growth already present in the wood, I consider this the lower limit. Temperatures up to 212 I". or, higher may be used. vIn the latter case, the steam or vapor should be of 100% relative humidity.

' Th'e length of time required for the water treatment depends upon the size of the material to be treated and would be from two hours for verythin stock to approximately two days for very 35. thick material. Necessarily the time is adjusted in accordance with experience based upon the treatment of materials-in varying sizes.

When the wood has been subjected for a sunlcient time to the eflect of the hot water, so th t 4 the wood cells contain a sufllcient quantity 3;-

wa'ter, the wood is immediately su l cted to inimersion in a suitable solution containing the ma- ,erial with which the wood is to be impregnated.

The time of immersion will vary as in the initial 6 treatment, depending upon the thickness of the wood. From one to ten days may be required,

ta tivezabsorption of toxic and flreprooflng agents, and the depth 01 chemical penetration desired.

A large variety of materials may be used for in the moisture content ofthe wood cells. The.

temperature at which the initial treatment is depending also on the concentration ofthe ch'em-v icals in the treating solution, the desired quantitthe treatment of wood in accordance withjthe invention, and the treatment may be in one or two stages, depending upon the character of the materials used. Thus, it is possible to select a chemical agent which may be toxic to wood destroying organisms or capable of rendering the wood resistantto nre. Numerous agents of this type are known, and the immersion of the wood tojnasol nofone oi thesematerlals forasufwood, following the initial treatment with hot I with hot water .to increase the moisture content flcient length of time will serve to impregnate the wood and accomplish the desired result. In some cases, however,,either the preservative or the fireprooflng eflect may be accomplished by immersing the wood in two diilferent solutions successively, so that the solutions will react within the wood cells to deposit a compound having the desired eflect. In some cases, both the preservative and fireproofing eflects can be secured by.the selection of suitable materials. In some cases, a third step may be introduced, involving the application of a reactive gas to the wood.

The two-stage treatment has the advantage that whereas water soluble solutions with which the wood may be impregnated may be leached therefrom when the wood is in contact with water, wet soil, etc., the formation of insoluble compounds within the wood cells ensures the reten-' tion'of the toxic or fireprooiing agent regardless of the presence of water. The two-stage operation for depositing insoluble compounds has been described heretofore in connection "with impregnation processes depending upon pressure, but in such cases the pores and checks in the wood are quickly plugged by precipitation of the insoluble material, and very shallow penetration is secured. By the resent. method the introduction of the insolu le compounds to the cells oi',the wood is assured because reaction does not ooel llsl imtil the two solutions meet within the c The following examples will illustrate the application'of the invention in respect to types of solutions which may be used to impregnate the water. The invention is not limited to the particular compounds mentioned. since as already indicatedit depends upon the initial treatment .of the cells so that diffusion through the walls thereof is made possible or accelerated. Furthermore, the temperatures, time of treatment and concentration of the solutions, are subject to wide variation, depending, as already noted. on a number of factors which must be considered in the practical application of the method.

- react to form a precipitate.

with respect .to the degree of impregnation, since it depends upon diilusion. The emciency of pressure in introducing solutions ormaterials into the wood is relatively low, whereas diffusion en- .sures the introduction of the materials'into the wood cells. Another advantage is the degree of control which can be employed by varying the factors such as time, temperature and concentration of the solutions used. Such control is not readily effected with pressure processes.

Various changes may be made in the procedure without departing from the invention or sacrificing the advantages thereof.

I claim:

1. 'The method of impregnating wood which comprises treating the wood with liquid water at a temperature above about 120 F. for a length of time suflicient to increase substantially the moisture content of the wood cells, and, while the moisture content of the wood cells is substantially increased, immersing the wood in a water solution of the material with which the wood is to be impregnated, and permitting the water solution of g the impregnating material to diil'use into the cells of the wood.

2. The method of imp e ating wood which comprises treating the wood at atmospheric pressure with liquid water at a temperature between about 120 F. and 212 1''. for a length of time suflicient to increase substantially the moisture content of thecells thereof, and, while the moisture' content of the wood is substantially in creased, immersing the wood in two successive aqueous solutions, the compositionsof which are such that they reset to'form a precipitate, and permitting each of said successive solutions to diffuse into the cells of the wood where they 3. The method of impregnating wood which comprises treating the wood with liquid water at a temperature above about 120 F. for a length of time suflicient to increase substantially the The method as herein describedhas numerous .Tims, Tlmom Tomper- Tmmltcriel =-Prsliminary treatment :23 Toxic solution and concentration toxic i g solution l treatment solution sxsmrtas or woop rasssavmd TREATMENTS 1) man" 12" 18 w ig ite t) 1dr 'u 1: ch v Hugs to m X X O N w. hemlock :2": wfinr not m 19% sincchloride 48 so EXAMPLE or r'maraoormo 'rasa'ruen'r vueamam museum Watulm' r. m)-.-..-.-. 11 48 0o spurts-or oomsr'mrron rmaraoormo mp rasssavmo Thurman-rs m 1'2" s'1;;-. w and. is use; sine amase im monosmmo- 4s e0 i rnh mvhmm anagram.ons-srsosram'rzupn'r'roa sornrmsraoormd am: rassaavmo poem-m2"; ir'xs' wmmr. (hot). 1s h rniation-hummus is co n f I fl-immcnoammonmmphosphatc....

Alternative step mounts by mm in ammonis at! l a I This wood anadrying contains line chromats, sinc ammonium phosphate, ammonium phosphate and ammonium chloride.

content of the wood cells, immersing the wood in a water solution of zinc chloride while the moisture content of the cells thereof is substantially increased, and permitting said water solution to difluse into the cells of the wood.

4. The method 01' impregnating wood which comprises treating the wood with liquid water at a temperature above about 120 F. for a length of time sumcient to increase substantially the moisture content of the wood cells, immersing the wood in a water solution of chromated zinc chlo- -ride while the moisture content of the cells thereof is substantially increased, and permitting said water solution to' difluse into the cells of the wood.

5. The method of impregnating wood which comprises treating the wood with liquid water at a temperature above about 120 F. for a length of time sufllcient to increase substantially the moisture content oi the wood cells, immersing the wood in a water solution of mono-ammonium flcient to increase substantially the moisture content of the cells thereof, immersing the wood successively in aqueous solutions of chromated zinc, chloride and mono-ammonium phosphate while the moisture content of the cells thereof is substantially increased, and permitting the wood to remain in each of said aqueous solutions for a length of time suflicient for them to diffuse into the cells of the wood, whereby a precipitate is formed in the cells oi! the wood.

RICHARD NEWTON HAMMOND. 

